The present disclosure relates to an electron mediator, and more particularly, to an electron mediator applicable to an electrochemical biosensor. In addition, the present disclosure relates to electrochemical biosensor employing an electron mediator.
Biosensors are analytical sensors measuring a concentration or presence of a biological analyte. Examples of the biological analyte include glucose, cholesterol, lactate, creatinine, protein, peroxide, alcohol, amino acid, glutamic-pyruvic transaminase (GPT), and glutamic-oxaloacetic transaminase (GOT). An electrochemical biosensor detects the flow of electrons generated by the electrochemical oxidation or reduction of an analyte.
A representative example of biosensors is a blood glucose sensor. An electrochemical blood glucose sensor may include, for example, a working electrode and a counter electrode formed on an electrical insulating substrate; and a detecting reagent layer contacting the working electrode and the counter electrode. The detecting reagent layer in the electrochemical blood glucose sensor may include, for example, a glucose oxidase or a glucose dehydrase; an electron accepting coenzyme; and an electron mediator. When blood containing glucose is in contact with the detecting reagent layer, the glucose is oxidized by the glucose oxidase, forming electrons. The formed electrons may be transferred to the working electrode through the electron accepting coenzyme and the electron mediator. An ampere meter externally connected to between the working electrode and the counter electrode may detect a flow of electrons to measure oxidizing current of glucose. From the oxidizing current of glucose, the glucose concentration in the blood may be analyzed.
Most of the oxidases, dehydrases, and electron accepting coenzymes generally do not have ability or are very weak ability to directly transmitted electrons to an electrode. Therefore, the detecting reagent layer in the electrochemical biosensor needs to include an electron mediator. Examples of the electron mediator may include potassium ferricyanide (K3Fe(CN)6), ferrocene, ferrocene derivatives, quinone derivatives, phenazine-methosulfate, methoxyphenazine-methosulfate, phenazine methyl sulfate, and dichloroindophenol. In particular, in the case of disposable blood glucose sensor, potassium ferricyanide (K3Fe(CN)6) is most widely used as an electron mediator. Potassium ferricyanide (K3Fe(CN)6) may be easily deteriorated by light, temperature, and humidity. Thus, in the case of long term storage, it is known that the precision of the biosensor decreases (refer to A Disposable Electrochemical Glucose Sensor Using Catalytic Subunit of Novel Thermostable Glucose Dehydrogenase, The Open Biotechnology Journal, 2007, 1, 26-30).
The electron mediator may serve to rapidly carry out electron transportation from an enzyme-coenzyme complex to an electrode. The enzyme-coenzyme complex obtained electrons from the analyte may be oxidized, transferring electrons to the electron mediator. The electron mediator, which received electrons from the enzyme-coenzyme complex, may be reduced. The reduced electron mediator may be oxidized to transfer electrons to the working electrode. Oxidation of the electron mediator may be carried out by the voltage applied to the working electrode (the voltage is with respect to the counter electrode). The voltage that may most effectively oxidize the electron mediator may be referred to as a working potential. The working potential may change depending on the combination of the electron mediator, the enzyme-coenzyme complex, and the electrode material.
It is noted that, if the working potential is excessively high, the working electrode may directly oxidize other materials rather than the analyte. Accordingly, an oxidizing current may be detected, which is greater than the oxidizing current that represents the actual concentration of the analyte. Accordingly, the concentration of the analyte may be determined to be greater than the actual concentration. Therefore, the working potential of the electron mediator needs to be lower than an oxidation voltage of materials other than the analyte.
Thus, the working potential of the electron mediator is required not only to be compatible with a selected combination of the enzyme-coenzyme complex and the electrode material, but also lower than the oxidation voltage of materials other than the analyte. However, it is very difficult to obtain an electron mediator that satisfies these requirements. It is because that a known electron mediator has an oxidation potential that is uniquely fixed. In addition, it is because that it is difficult to synthesize a new electron mediator that may exhibit the desired working potential and excellent electron transfer efficiency.
In order to achieve excellent electron transfer efficiency, the use of a combination of two different electron transfer materials as an electron mediator has been proposed (refer to: U.S. Pat. Nos. 4,898,816 and 8,057,659). In this case, the first electron transfer material may serve as a mediator that receives electrons from the enzyme-coenzyme complex, and the second electron transfer material may serve as a shuttle that transports electrons to the electrode. However, even in this case, it was not easy to adjust the working potential of the electron mediator system including the first electron transfer material and the second electron transfer material.